It wasn't that Husband could not believe what she said.... it was more of how quickly she was thinking. This took place in the car, as he was trying to buckle the kids in.
Bird: Daddy, you need to tell Bug you're sorry.
B: You weren't very nice to him.
B: You said he was (drops voice to a whisper) stupid.
H. I didn't say stupid!
B: Well you just said it, so tell him you're sorry.
It's not very often that Husband is at a loss for words.